| The development of thermoelectric (TE) refrigeration meets many new opportunities, such as pressing environment pollution and energy conservation, accurately controlling temperatures in the following fields: electronics, biology, medicine and so on, and integration of new material and other correlating technology, An increasing number and variety of promising TE products have been reported for specific applications in military, instrument, medicine and other fields. Former investigations are mostly in the development of high quality TE materials and modules, while works on the optimization of TE refrigerating systems were scarce. In this dissertation, the progresses of TE refrigerators in the past 40 years were firstly reviewed, and the recent advance in the past 10 years were especially stressed. The thermodynamic characteristics were analyzed for an ideal TE refrigerator, which is externally reversible and internally irreversible. The physical mechanisms were compared between TE refrigerators and mechanical refrigerators. Their circulation of energy carriers (electrons or refrigerants) and corresponding energy levels present comparability although their circulating patterns differ considerably. Three eco-friendly refrigeration systems: TE refrigeration, magnetic refrigeration and adsorption refrigeration were compared in the aspects of principles, thermodynamics, practicability and developments. It is found that TE refrigeration is the most well-developed, applicable and competitive technology. In this dissertation, a dimensionless thermodynamic model of TE refrigerating system was founded for steady running conditions, and its performances were analyzed by numerical calculations for different varying parameters including merit figure, temperatures of heat mediums, electrical currents and heat resistances. The correlations between above parameters were also discussed. The various irreversibility, such as Joule heat, Fourier loss and finite heat transfer, were analyzed for real TE thermodynamic cycles and energy conversion. The consistency of thermodynamic characteristics was analyzed between TE refrigerators and mechanical refrigerators. The irreversible losses of a TE refrigerating system represent the typical losses of general two-source refrigerating system. Its finite heat transfer, Joule heat and Fourier heat are respectively corresponding to the irreversible heat transfer, friction loss and heat leak of compressing refrigerating system. The conclusions are of great significance for optimizing real TE refrigerating systems. A TE refrigerating experimental system was founded in TE laboratory of Hunan University; it utilized water as heat mediums. The optimum allocation of heat transfer surface and measures intensifying heat transfer were discussed and quested for high performances. Experiments were performed with varying parameters as following: (1) flow-rates of heat mediums; (2) electrical currents; (3) temperatures of heat mediums; (4) directions of heat mediums. A panel-type separating thermo-siphon was originally developed. It offers a new approach for heat transfer intensification of TE refrigerating systems. Experiments were performed on structure type, working medium, optimum filling-rate and characteristics of heat transferring. The situations of energy consumption were analyzed for hot water in different buildings. Two novel TE heat-pump instantaneous waters and a novel TE heat-pump clothing dryer were originally developed and investigated in the TE laboratory. The originalities of the dissertation are mainly in the following: (1) Two new concepts, the permissive temperature ratio and the favorable working region, were presented as optimizing rules for TE refrigerating systems. It was pointed out that temperature ratio may better include the effect of temperatures on the performances of a TE refrigerating system than temperature difference. The optimum working point should be (εq)max, it is different from the conventional maximum points of refrigerating coefficient and capacity. (2) Another new concept, the performance pinnacle, was presented as a theoretic evidence for development of efficient TE refrigerating or heat-pump systems. (3) A panel-type separating thermo-siphon was originally developed. It offers a new approach for heat transfer intensification of TE systems. (4) Experiments offered datum reference for development of efficient TE refrigerating or heat-pump systems under near room-temperatures. The two novel water heater prototypes, compared to electrical water heaters, can reduce more than 40% or 38% of the power consumption. (5) A TE heat-pump clothing dryer was originally developed. In comparison with conventional electrical clothing dryers, it can reduce about 35% of the power consumption. As for application prospects, new materials and synthesis techniques have reawakened interest in the use of TE technology for CFCs will be prohibited as refrigerants in the whole world before long. It offers a constructive technological approach for developing distributed refrigerating or air-conditioning system inbuildings. It also offers new ideas for dispersed waste energy recovering and low-grade energy utilization. It was expected that TE cooling would be one of leading approaches of cooling electronic components. Since the merit figure of TE materials is unsatisfactory, the efforts of optimizing TE refrigerating systems should centralized on heat transfer intensification, and optimizing allocation between cold and hot sides. The system should run in the favorable working region, and the optimum working point should be (εq)max. In addition, energy recovering is of great significance to improve performance of a TE refrigerating systems.
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